1. Field of the Invention
The present invention relates to a control system for a brake vacuum pump, and more specifically, concerns a control system for the brake vacuum pump, the system performing the driving control of the vacuum pump that is connected to a vacuum chamber of a brake booster into which a negative pressure occurring in an intake manifold of an engine is introduced, and that assists the introduction of the negative pressure into the vacuum chamber.
2. Description of the Related Art
In a braking apparatus for a vehicle, the brake booster has been widely used for introducing the negative pressure occurring in the intake manifold of the engine into the vacuum chamber, and boosting a depression operating force against a brake pedal by making use of the negative pressure accumulated in the vacuum chamber.
In recent years, with a trend toward placing a throttle valve under electronic control for the purpose of improving exhaust emission characteristic, operating conditions in which a sufficient negative pressure is difficult to generate in the intake manifold, are on the increase. Furthermore, in recent times, for the purpose of enhancing the braking force in response to the upsizing of vehicle, there is a demand to keep the vacuum chamber in a deep negative pressure state (i.e., a low pressure state).
To cope with these situations, many techniques for assisting the introduction of negative pressure from the intake manifold to the vacuum chamber using the vacuum pump, have been proposed. For example, Japanese Unexamined Patent Application Publication No. 9-177678 discloses a technique for performing a driving control of the vacuum pump in response to the pressure state (absolute pressure or relative pressure) in the vacuum chamber (vacuum tank).
However, an arrangement that merely performs a driving control of the vacuum pump in response to a pressure state in the vacuum chamber as in the art disclosed in the above-described Japanese Unexamined Patent Application Publication No. 9-177678, may excessively operate the vacuum pump.
For example, when the negative pressure in the vacuum chamber temporarily becomes shallow (i.e., when the pressure becomes high) by a user performing repetitive braking operations in a short time, the vacuum pump may undesirably be operated even though the negative pressure can be quickly accumulated up to a predetermined value by using only the negative pressure occurring in the intake manifold.
Moreover, even in a situation not requiring so much braking force, such as before a starting state immediately after the startup of the engine, or in a constant running state at a relatively low speed, the vacuum pump may unfavorably be operated.
To overcome the above-described problems, the present invention is directed to a control system for the brake vacuum pump, the system being capable of accumulating the negative pressure required for the vacuum chamber, without excessively operating the vacuum pump.